The Wired article speaks of Shawyer's EMDrive, which has been around for some time, and at first appears to confuse the EMDrive with a different technology Dr. Harold "Sonny" White of NASA has been working on for some time.
The tech report clears things up a bit. The test results are showing anomalous thrust, however NASA is reticent to attribute the thrust to Shawyer's theory of how it operates, which would violate conservation of momentum (hence the "impossible" in the title.
What the technical report says is something far more interesting. Dr. White has been working with several different test articles which use electromagnetic forces to increase the rate of virtual particle pair production in the quantum vacuum, then using the virtual particles during their very short time of existence as reaction mass. In other words, it is a reaction drive, but instead of carrying reaction mass in the tank, the investigators are trying to use mass borrowed from quantum vacuum plasma to generate a small, but measurable, amount of thrust.
The final sentence of the technical report contains the salient material:
"Test results indicate that the RF resonant cavity thruster design, which is unique as an electric propulsion device, is producing a force that is not attributable to any classical electromagnetic phenomenon and therefore is potentially demonstrating an interaction with the quantum vacuum virtual plasma. Future test plans include independent verification and validation at other test facilities."